ATHENS, Greece — When you're trying to fathom a mangled relic of very old hi-tech, it helps to have the manufacturer's instructions.

For over a century since its discovery in an ancient shipwreck, the exact function of the Antikythera Mechanism — named after the southern Greek island off which it was found — was a tantalizing puzzle.

From a few words deciphered on the twisted, corroded fragments of bronze gears and plates, experts guessed it was an astronomical instrument. But much more remained hidden out of sight.